Looking for help resolving a persistent knock problem. I have a stock '87 GN with 68,000 miles.
At least 20,000 miles or so ago, I started getting a nasty hard knock at high RPMs. When this happens, the stock boost gauge is pegged into the red. At one point it sounded like a machine gun, RAT-TAT-TAT-TAT!
Not sure where to begin with the troubleshooting. I've done the following with no luck: Changed the wastegate solenoid and Y hose assembly; tried new spark plug wires and coil pack; inspected and regapped spark plugs to .035; installed the feeder line to my fuel pump.
Installing the Red Armstrong 93 chip and running 110 octane helped only a little--it gave me a few more RPMs before it started knocking, but the pounding was just as bad if not worse when it happened.
Any help would be greatly appreciated. I can't enjoy my ride, and I cringe every time I really want to get on it. It's all I can do to restrain my foot to prevent it from happening. I honestly don't know what WOT feels like, nor do I know what my car is really capable of. I'm afraid I'm going to toast my engine before I'll ever get this resolved.
Thank you,
Greg
Forgot to mention also:
1. I have a heated 02 sensor installed with less than 20K miles on it. I religiously wait at least 20 seconds with the key on before cranking over the engine to allow the 02 sensor to heat up.
2. I replaced the crank sensor awhile back because it fell apart. I installed the new GM replacement.
3. I occasionally run 100LL AvGas with the test pipe in place of the cat. The cat has seen only about 5-10K miles with a 2:1 mix of 2 parts 91 unleaded to 1 part 100LL AvGas.
4. I failed emissions for the first time last week. It was hydrocarbons. Our limit in Arizona is 1.60 grams/mile; I failed at 2.03. I had the 93 chip, the TPS enhancement, and volt booster installed at the time. I've since taken out the TPS enhancer, cleaned and inspected my spark plugs and regapped them to .035 (they were all between .005 and .010 off), and put the stock chip back in. I plan to leave the volt booster in. (I've passed emissions before with the 93 chip in and 1/3rd AvGas! This was the first year I've not passed. The only major difference was the TPS enhancer.) Not sure what else I can do. I'm thinking the EGR valve could be at fault, but have no idea how to confirm.
I'm concerned that either: a) this knock problem I'm seeing is somehow related to my failing emissions, or b) my cat is toast.
I'm ready to take it back to retest emissions, but I'll try to hold off for a few days to look for input from the group here.
Thanks,
Greg
Here's a place you can start. Hook up a fuel pressure guage to the fuel rail. Set it up so you can see the guage while road testing. the fuel pressure should increase when the boost increases. If it goes the opposite way then you got a fuel supply issue which may be causing you to run lean and thats why your getting knock. If you find its a fuel supply issue then try replacing the fuel filter first.(cheapest). Hope this helps, good luck!
Could be you've wiped a cam. I had a BAD knock and popping problem with my T and that's what it turned out to be. Like Daniel said, you need to verify fuel pressure at boost, and getting some sort of scan tool wouldn't hurt so you know whats going on. How much boost are you running? If you don't have an aftermarket boost gauge, GET ONE! The stocker is basically junk, they are notoriously innacurate. The fact that it's pegged when you have the problems might point to excessive boost that you are unaware of. Overboostng and fuel problems are the most frequent causes of high end knock, and without verifying these issues are not the cause, it's like peeing into the wind trying to figure the problem out. Have you added a hotwire to the fuel pump? Is the pump stock? Even though your car is basically a low mile car, it's still 17 years old and stuff wears out. The stock pump was barely adequate when it was new and the stock pump wiring has been proven to have issues. Check out the above mentioned issues, then get back to us and let us know what you found.
Fast Freddie
Any scan tool or data log readings?
Dean
Thanks for the replies so far.
I do have a feeder line ("hotwire") running to the stock fuel pump. I also replaced the stock fuel sock in the tank awhile back--definitely needed it badly at the time, and I flushed the tank. I've also replaced the fuel filter a couple times.
A neighbor of mine, an avid GN owner, checked my fuel pressure at idle a few months ago and said it looked good, but we didn't do a road test. He's hard to nail down, but he did commit tonight to help me out for a road test, hopefully this week. He said we could tape the gauge to the windshield. He also has a scan tool; I'll try to get his help to collect some data.
I do not have an aftermarket boost gauge, yet.
I'm doubtful that I have a bad cam--I assume that's what you mean by "wiped a cam." Yeesh. I don't even want to think about it, but I won't rule it out yet either. The car runs smooth and solid 80% of the time. It's when I want to really get on it that I'm having this problem.
Hey... the toasted cam thought made me think of something else... What about a valve adjustment or new springs? I haven't had the valves adjusted for at least 30,000 miles. Come to think of it, I bought the car with 33,400 on it and can't remember if I ever did have the valves adjusted.
A scan tool has been a bit cost-prohibitive for me... Was hoping to put that kind of $ toward an aftermarket boost gauge, adj. fuel pressure reg and gauge, adj. wastegate actuator, etc., etc.. But, I realize now that I'm not ready for all that yet. Besides, it seems a bit pointless without having a scan tool or the knowledge/ability to dial in the performance. Right now I have just enough knowledge to be VERY dangerous.
What do you guys recommend? TurboLink looks like the way to go, as I do have a laptop, but I don't have the first clue how to use any scan tool or interpret the data, let alone add the $300+ to the unknown cost to resolve my problem once I do isolate it. I'm a fair mechanic, a helluva computer whiz, and quite analytical in my own right, but I'm a total newbie at engine analysis. I'm willing to learn, though.
No matter what, this knock problem needs to be resolved first, so... if you guys really think providing data would help you help me, just say the word, I'll spring the bucks for TurboLink ASAP, unless there's a more suitable tool that you'd recommend. I figure I'll spend at least that on a mechanic to resolve the problem for me, so what the heck.
Thanks,
gd
Non adjustable valvetrain, but yes, the springs will need replacement if they haven't been already.
IMO, a scan tool is the first thing someone with a TR/TTA should get (~$250-500+). Best case would be a data recorder. I know it is a big $$ item, but nothing like the cost of an engine. Think of it as an insurance policy. This would be followed by a CCCI Ignition Simulator from Casper's (~$120), a boost gauge (~$80-100 with a pillar pod) and DIY adjustabe WG actuator (~$1), and an ADJ FPR & FP gauge (~$200)... in that order as funds allow. Gotta get it running right for a proper baseline before you start buying go-faster-goodies.
As for interpreting the data, first learn some of the basics, like what the various sensor normal operating ranges are, and how components work. Much of what you need to learn is here on this site, but there is more info "out there" if it isn't explained well enough here for you to understand at first.
As to which ST/DR to choose, it is up to you. I usually recommend SM as a first purchase as it would (typically) always be there in the car every time you go driving, and you don't need to have a laptop, but since you have one, perhaps not. The only problem with SM is it isn't a data recorder. For a data recorder TL is great, particularly if you are using a newer laptop, but lately I have used DS far more often for the higher data rate. A lot can happen in a short period of time, and at 18+ frames of data per second, DS captures significant amounts of data. Here's more of MO on scan tools: http://home.pacbell.net/sfnelson/turbo_regal_scantools.htm .
Dean
Very good information, Dean. Thank you. I'm checking it all out now.
After regapping the sparks and reinstalling the stock chip and cat, the car is definitely running noticeably better through the gears (to a point--still can't go WOT without the knock). For example, that crisper 1-2 shift "bam!" that I love is back. But two interesting "symptoms" have returned that I forgot about long ago... 1) idle is rough, and 2) I experience a very annoying hesitation on starts, especially when the engine is cold. These symptoms have been with the car since the day I bought it. Reinserting the TPS sensor seems smoothes both of those out, but it seems to compound the high-end knock problem.
Just FYI in case this information can add value to the diagnosis for the high-end knock problem.